1. Field of the Invention
This invention relates generally to methods for storage of waste products, and more particularly to methods of storage of hydrophobic waste material and concentrated aqueous salt solutions.
2. Prior Art
In today's industrialized society, disposal of hazardous waste materials has become a major concern. Because of the wide variety of waste materials involved, varying degrees of difficulty have been encountered in finding methods to safely treat these waste materials prior to storage or transportation. Prevention of water infiltration into porous soil surfaces is relatively easy to accomplish by treating the soil with water soluble polyelectrolytes. These soil conditioning processes are described in the following U.S. patents:
______________________________________ U.S. Pat. No. Inventor Issue Date Title ______________________________________ 2,703,276 Hedrick, et al 3/01/55 Soil-Conditioning Fertilizer 2,751,367 Yost, et al 6/19/56 Firable Poly- acrylate Powders 2,868,758 Edgar B. Baker 1/13/59 Method of Improving Soil 3,016,713 John M. Deming 1/16/62 Method of Treat- ing Soil With Aqueous Slurry of Lattice Clay and Anionic Poly- electrolyte 3,772,893 Louis H. Eilers 11/20/73 Soil Sealing Method 4,255,067 John C. Wright 3/10/81 Disposal of Liquid Waste and Recov- ery of Metals Therefrom 4,277,203 Reed, et al 7/07/81 Soil Stabiliza- tion Materials and Methods 4,291,069 Richard J. Pilny 9/22/81 Rendering Porous Structures Imper- meable By Treat- ment With Gell- able Amine Poly- mers 4,350,461 Valiga, et al 9/21/82 Multiple Waste Disposal Vaults 4,362,434 Valiga, et al 12/07/82 Permanent Dis- posal Vault For Hazardous Chem- ical Waste Mate- rials ______________________________________
These methods have been reasonably successful in immobilizing dilute solutions of water soluble compounds, but are not effective in immobilizing concentrated salt solutions or non-water soluble compounds. Other methods such as those disclosed in U.S. Pat. No. 3,196,619 Shock, issued Jul. 27, 1965 and entitled "Method For Disposing of Harmful Organic Waste Materials," and U.S. Pat. No. 4,255,067 Wright, issued Mar. 10, 1981 and entitled "Disposal of Liquid Waste and Recovery of Metals Therefrom" have been tried, but have not met with sufficient success to replace the present practices in the industry which include the storage of the waste in metal drums and the like, or the building of conventional clay-lined beds to hold the wastes.
Clay liners were considered adequate for the construction of hazardous waste landfills because they provided relatively secure confinement of aqueous wastes. However, clay liners are subject to tension cracks, and attack by both organic materials and brines. When clay barriers are used with hazardous waste mixtures, permeation of the barrier can occur rapidly as the clay barrier develops cracks due to geological or chemical stress. To assure protection of groundwater against potential contamination, a containment barrier technology involving double liner systems has emerged. Impermeable plastic films (geomembranes) are laid on clay barriers to form liners with double security, which is necessary because the geomembranes are also subject to puncture and attack by waste mixtures.
A number of materials have been evaluated as primary liners for landfills, but the number of acceptable geomembranes for this application is relatively limited. Consideration of the design requirements pertaining to liners reveals the cause for the limitations. The requirements include:
1. All newly sited landfills must have liners that are designed, constructed and installed to prevent any migration of wastes out of the unit to the adjacent subsurface soil, groundwater or surface water at any time during the active life of the facility. Clearly, the geomembrane must be selected to contain the most chemically aggressive material in the landfill for extended periods of time, preferably for decades.
2. Liners must be constructed of materials that have compatible chemical properties and sufficient strength and thickness to prevent failure due to pressure gradients, including static heads and external hydrogeologic forces. In addition the liners must be capable of withstanding adverse climatic conditions, the stress of installation and the stress of daily operations.
3. The liner must be placed upon a foundation or base (secondary liner) capable of providing support to the liner and resistance to pressure gradients above and below the liner. The foundation must be designed to prevent failure of the liner due to settlement, compression or uplift.
The design requirements for these liner systems is to achieve and retain a continuous, deformable and relatively homogeneous medium which minimizes the hydraulic conductivity (currently less than 1.times.10.sup.-7 cm/sec) during the lifetime of the facility and hence prevent migration of the contaminents. Although geomembranes have gained increasing use in such facilities, their use in practice are associated with problems pertaining to:
1. puncture and tearing/pullout of the seams, PA1 2. deterioration of the integrity of the geomembrane in contact with leachates containing a high amount of organic contaminents. Therefore, it is of common practice to use geomembranes in conjunction with compacted earthen barriers (secondary liners). The major practical difficulties in achieving the design criteria with earthen barriers are identified as:
a. the effect of structural discontinuities of the in situ hydraulic conductivity of compacted earthen barriers, PA2 b. volume changes induced by different leachate composition and the resulting post construction tension cracks, PA2 c. disruption of the integrity of the earthen barrier due to excessive differential or total settlements, PA2 d. incompatibility in deformation behavior of the relatively thin extensible geomembrane and stiffer earthen barriers.
Assured long term retention of diverse chemical wastes is difficult to achieve with geomembranes composed of single materials supported by compacted clay secondary liners. As more complex mixtures of materials are combined into a single liner, the compatibility and ultimately the long term stability of the primary liner must be questioned. Most of the major manufacturers of geomembranes are actively pursuing research on new liner compositions in an effort to find an acceptable solution to the retention problem. However, little attention has been paid to the potential enhanced security which could be contributed by the secondary liner.
Harriett, U.S. Pat. No. 4,534,925 discloses a method of mixing non-hydrated bentonite clay with polypropene, polybutene or mixtures thereof. The mixture may be extruded in the form of sheets to provide a water barrier. The above composition has several drawbacks as a waste pit liner including susceptability to attack by organic solvents, requirements of at least 15% by weight of polymers and need for non-hydrated clay as a starting material.
Another treatment method for liquid waste is encapsulation. Examples of encapsulation can be found in Filter et al, U.S. Pat. No. 4,405,512 and Drake et al, U.S. Pat. No. 4,382,026. Filter, et al show how to form an emulsion of a resin and a waste liquid followed by curing the resin to encapsulate the waste liquid. Drake et al show an improvement over Filter et al in which the organic components of a liquid waste are absorbed by swellable polymer beads thereby preventing the organic components from plasticizing the resin. In both of the aforementioned patents, all of the liquid waste, aqueous and organic, is encapsulated with no volume reduction. Drake et al teach the use of non-coalescent, gelled polymer particles, recommending gentle agitation and particles having a size range from 0.1 to 1 mm in diameter. Wicking agents are recommended to avoid a prohibitively long organic liquid uptake time by the beads.